I wouldn’t say the state of the art is particularly great, but interestingly enough server-side rendering + JS sprinkle is exactly what many modern frameworks l

I wouldn’t say the state of the art is particularly great, but interestingly enough server-side rendering + JS sprinkle is exactly what many modern frameworks like Marko are going back to. They provide some opinionated/convenient ways to author code but deliver fully server-side rendered HTML. They use fancy means to detect where interactivity is needed, and only ship JavaScript to the browser for those components. In fact, they make what you describe easier to achieve. When you do it on your own, it’s up to you to ensure one piece JavaScript doesn’t mess another piece up, it’s up to you to sync back-end with front-end—but with a good framework you get encapsulation, bundling, and typing with compile-time checks (if you removed an attribute from some object server-side but forgot to update the client side, your build will fail with a useful error message before you can deploy it).